I broke the one way valve that is on the main vacuum line between the vac pump and the brake booster. Not a biggie as the part is readily available. Some questions though. This seems to be the true heart of the vac system, engine doesn't shut off, door locks are funky etc. On the line there are two three-way rubber connectors leading on to the maze of vacuum lines. One leads to the transmission. Now, I have a transmission that shifts HARD at low, bumper to bumper speeds. I think that means too low vacuum at the tranny solenoid. How is vacuum regulated to the tranny? Is there an adjuster someplace or is this an orifice controlled system? I'm going to try some mityvac work. When I pull a vac with a mity vac on any line should that circuit alwys be able to hold vac for at least a little bit? Where's the vacuum storage module in the trunk? How well should that hold vac?
Anyway, new part should fix a lot in a couple of days.

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1985 300D 197K - Semi-Daily Driver Diesel
1998 Volvo V70 AWD 226K - Daily Driver 2
1998 Volvo S70 140K - Wife's DD
2003 GMC Sonoma ZR2 Option - Rusty Truck
THE BABY 1958 220S Sedan 66K All original, never restored and never will be.

The transmission vacuum is controlled by the VacuumControlValve, a round device with a line and a green damper coming out of the top, then going to the transmission modulator.

Yes, I think your problems will vanish once the vac line has been repaired.

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83 SD

84 CD

The VCV, that the thing on the left side fender hump under the hood? Has some curved, tight fitting rubber lines? Do these go bad? Anyway to determine if the thing is OK?
Thanks much

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1985 300D 197K - Semi-Daily Driver Diesel
1998 Volvo V70 AWD 226K - Daily Driver 2
1998 Volvo S70 140K - Wife's DD
2003 GMC Sonoma ZR2 Option - Rusty Truck
THE BABY 1958 220S Sedan 66K All original, never restored and never will be.

That item with the green dashpot at the top, behind the IP.

The 85's have a somewhat different set up, but the VCV is the same, just more vac lines.

That round pointy thing does come off and it can be adjusted, but wait until you have the new part installed, then take a vacuum reading.

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83 SD

84 CD

I need to adjust my transmission vacuum. When I accelerate moderately I get flare going into 2nd and 3rd. If I accelerate harder, then I get smooth shifts.

Does anyone remember which way to adjust it to increase/decrease vacuum to the VCV?

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85 300D Turbo